While preparing to remove the fenderwell liners, I found a nut lying on the lower control arm and a link that was not hooked up. This link is only on the driver's side. What does it do?

Presuming that you have the HID option...

What DonL said. It's for the headlight leveling system.

Thanks. I will have to check out the hardware in the rear to make sure it is connected.

I had the same thing the first time I took my wheels off. Although in my case, the nut was had tightened on the bolt, just not connected to the arm. My rear one was connected. I can only guess that it was undone for some sort of work and then forgotten to be put back. Perhaps the same happened to yours, but your nut/bolt came undone?

There was no bolt. Only the nut.